Impotence, or lack of a man's ability to have sexual intercourse, is often the subject of parlor humor, but millions of men suffer from this condition, regardless of age, Impotence is generally characterized by an inability to maintain a penile erection.
Causes of impotence are numerous. It may be atonic, due to paralysis of the motor nerves (nervi erigentes) without any evidence of lesions to the central nervous system. Conversely, it could be paretic as a results of a lesion in the central nervous system, particularly the spinal cord. Alternatively, it could be psychic, and dependent on a mental problem or instability. Finally, it could be symptomatic, due to some other disorder, such as injury to nerves in the perineal region, by virtue of which the sensory portion of the erection reflex is blocked out.
Whether the impotence is absolute, involving all sexual modalities, total, affecting all sexual function, though not necessarily libido, or partial, affecting the rigidity or duration of the erection, or whether the cause of impotence is organic, due to structural changes, disease, or some demonstrable functional impairment anywhere in the sexual system, psychogenic, due to old age or sexual satiation, the result is the same: at least partial inability to engage in sexual activity due to the lack of an adequate erection.
Impotence may be defined more fully, however, as the inability to develop or sustain an erection of the penis sufficient to conclude coitus or orgasm and ejaculation to the male's own satisfaction. Impotence treatment methods are generally, however, concerned with the erection aspect, and not ejaculatory impotence, which is relatively rare.
The body of the penis is surrounded by a cornified layer of skin. Blood is supplied through the dorsal artery and removed through the dorsal vein. The urethra is surrounded by a fibrous compartment known as the corpus songiosum, which permits urination and provides a path for semen during ejaculation.
The corpora cavernosa form the chief part of the body of the penis, and at their rear portion they form the crura where the penis is firmly connected to the pelvis and ischium. The corpora cavernosa are surrounded by a fibrous sheath having exterior and interior portions respectively. The portion of the corpora cavernosa within the fibrous sheath consists of a sponge-like tissue of arveolar spaces freely communicating with each other and filled with venous blood. This space may be thought of as a large cavernous vein. The arteries bringing blood to these spaces are the arteries of corpora cavernosa and branches from the dorsal artery, which perforate the fibrous sheath along the upper surface thereof.
Under the proper stimulus, the penis becomes erect when the corpora cavernosa become widely dilated with arterial blood, thereby causing these tissues to become less flaccid. At the extreme side of the corpus cavernosum, tiny veins are connected to nerve endings, and, upon the proper stimulus, the veins assume a position so as to block outflow of blood from the corpus cavernosum. This mechanism is psychologically controlled.
The turgor phenomenon is generally caused by an action of the autonomic nervous system. The autonomic nervous system consists of two divisions, the sympathetic nervous system and the parasympathetic nervous system. In a healthy individual, activity by one of the two autonomic nervous system results in a physiological effect opposite to that of the activity of the other system. An autonomically-controlled physiological state is determined, at any time, by the relative degree of activity of the two systems.
The autonomic system controls the blood flow in the penis by means of peripheral nerves attached to the arterial vessels in and around the corpora cavernosa. During normal physiological activity, the sympathetic nerves maintain these arteries in a constricted state. As the man becomes aroused, his parasympathetic system releases certain chemicals, principally catecholamines such as norepinephrine and epinephrine, which inhibit the action of the sympathetic nerves resulting in relaxation of the smooth muscles surrounding the arteries and thus dilation thereof.
In the case of neurological problems, the nerves cannot convey the proper stimulus to either the arteries or the veins, This is the case with diabetics or patients with problems of the peripheral nervous system. In the case of a patient afflicted with arteriosclerosis, which often accompanies aging, the arteries cannot carry sufficient blood to the corpus cavernosum because of obstruction.
The most widely used therapy for treating impotence has been the implantation of penile prostheses. The simplification of the surgical technique, the obvious and rapid solution of the difficulties for intromission, and the popular appeal of prostheses all inhibited the search for pharmacologic intervention. However, recently, a great interest has developed in the use of a variety of agents for improving both libido and the quality of erections.
Many blood constrictive devices have also been proposed for producing and enhancing an erection. Typically, these are adjustable, tourniquet-like rubber band devices which are designed to fit tightly around the shaft of the penis and thereby restrict the flow the blood from the penis through the surface veins, as well as the deeper dorsal vein, to prolong an erection. There have been numerous attempts to solve this problem, but all exhibit various disadvantages to the user, and sometimes to the female partner, such as extreme discomfort during intercourse, to the extent that users might not achieve the desired usefulness as frequently as desired and to the extent preferred. All of the external devices previously proposed have the psychological disadvantages of being an impediment to actual intercourse, and the operational disadvantage that their duration of effectiveness is relatively short.
Impotence associated with androgen deficiency has long been thought by certain medical factions to be treatable by the administration of male hormones via synthetic preparations such as methyl testosterone and various esters, as well as a number of testosteroneaphrodisiac compositions. The relationship between testosterone levels and impotence has not been firmly established. However, the administration of exogenous hormones has several pharmacologic disadvantages. For example, methyl testosterone must be taken subcutaneously or bucally, and may cause severe toxic effects such as cholestatic jaundice. Parenterally administered testosterone esters, while less toxic and more certainly absorbed than methyl testosterone, have the drawbacks of intramuscular administration including additional pain, lack of complete absorption, and risk of deep and widespread infection. Additionally, long-term administration of these synthetic compounds may inhibit endogenous testosterone formation and spermatogenesis by suppressing pituitary gonadotropin, resulting in glandular tissue atrophy because of disuse.
Because of the uncertainty and the problems involved in the administration of testosterone in the treatment of impotence, there have been numerous nonandrogen attempts to treat the impotence problem, including treatments with yohimbine, damiana, ginseng, levodopa, hydergine, clomiphene, phosphorous, strychnine, and cantharides. Other drugs tested for treating impotence include bromocriptine, nitroglycerin, zinc, oxytocin, and lutenizing hormone-releasing hormone. These are generally administered orally with varying degrees of success, some with significant side effects.
Intracorporeal injections of papaverine have been investigated for some time, and this has become one of the more commonly used of the various pharmacologic agents. Alternatively, as disclosed by Latorre in U.S. Pat. No. 4,127,118, nonsteroidal agents, including an appropriate vasodilator, can be injected into the corpus cavernosa to cause an erection. Among the vasodilators that can be used are sympathomimetic amines or adrenergic blocking agents, or other agents within the histamine and epinephrine groups. The most obvious drawback to this type of treatment is the need for an infection whenever an erection is desirable.
Topical agents have also been proposed to induce an erection, such as disclosed in Voss et al., U.S. Pat. No. 4,801,587. The ointment disclosed therein comprises a vasodilator or alpha-blocker in an ointment base, along with a carrier. However, in this case, the ointment only includes an agent to dilate the arterial vessels, and there is nothing to constrict the veins to retain the blood in the corpora cavernosa.
Nitroglycerin paste has been widely used in the treatment of angina. Morales et al., in Urologic Clinics of North America 15:(1) 87-93, 1988, disclose the results of a double-blind, controlled randomized trial of nitroglycerin paste versus placebo paste under strictly controlled laboratory conditions. This study demonstrated that nitroglycerin transcutaneously administered enhances the quality of erectile episodes in the presence of an erotic stimulus and under laboratory conditions. An important consideration is the effect of the drug on the sexual partner, since nitroglycerin is readily absorbed by the vaginal mucosa. One case of secondary headache in the sexual partner of an individual who used nitroglycerin on his penis has been reported.